This invention relates to pulp refining apparatus, i.e. apparatus for producing and/or mechanically processing pulp, such as wood pulp and other fiber slurries. More particularly, the invention concerns a lining element for application to relatively rotatable backing members of a refiner, such as, for example, a face plate for a disc refiner.
A pulp refiner essentially is a milling apparatus used for producing pulp from wood chips or other fibrous raw materials and/or for processing pulp to modify the fibers to the desired condition. A common type of pulp refiner includes two relatively rotatable, concentric discs the confronting faces of which are lined with removable wear resistant face plates having a pattern of ridges and grooves. The lined refiner discs define between them a narrow annular clearance. The material to be refined is fed into this clearance at the center of the discs and is subjected to the refining action (i.e. the defibration of the wood and/or the conditioning of the fibers) of the ridges of the face plates as it flows radially outwardly through the clearance.
Face plates and other lining elements for pulp refiners are commonly cast from alloys of various types. Cast iron, stainless steel and other steel alloys containing nickel and molybdenum and various other ingredients are customary materials.
Lining elements for pulp refiners have to satisfy various requirements which are conflicting in some respects and which are difficult or even impossible to meet in one and the same lining element using the customary materials. For example, the lining elements should maintain an excellent and uniform refining action to be able to produce pulp of high and uniform quality throughout their life. Moreover, they should have high resistance to wear so as to have long life, as well as high impact strength to be able to resist the impact loads to which they may be subjected even in normal operation. A further desired quality is high resistance to corrosion and erosion. The material from which the lining elements is produced also should have good castability so that the elements can be cast in complicated shapes, and naturally the material should not be too expensive in relation to the properties of the finished elements.
A requirement related to the above-mentioned requirement for an excellent and lasting refining action is that the lining elements should be self-sharpening. This means that the lining element surfaces defining the narrow refining clearance, the working faces of the ridges, must not be polished too easily by the pulp, but must retain a certain limited, uniform roughness throughout the life of the element. Most known lining elements of alloyed steel require frequent regrinding of the working faces of the ridges, because these faces are rapidly polished by the pulp and because the edges of the ridges rapidly become blunt.